The present invention generally relates to a hot melt adhesive application machine. More specifically the present invention discloses a novel method and apparatus for supplying heat to the molten adhesive reservoir and providing heat to the molten adhesive discharge hoses and applicators. Further a unique and novel heated adhesive piston displacement pump mechanism is taught whereby the cost of manufacture of the pump has been reduced.
Heretofore, hot melt adhesive application machines basically comprised a heated reservoir from which the molten adhesive was removed by a piston displacement pump manufactured to exacting tolerances. In such a system the reservoir container is directly heated by any convenient means, whereby heat transfer is, by conduction, from the reservoir container into the reservoir of adhesive material. Therefore the reservoir must be maintained at a temperature above that of the molten adhesive to maintain heat flow into the molten adhesive since heat can only flow from a high temperature to a lower temperature. Since the reservoir container will typically comprise a relatively large surface area the reservoir shell represents a large heat conducting and/or radiating surface. Thus the outer surface of the reservoir shell must be heavily insulated to minimize heat loss from the reservoir to the surrounding environment. Nevertheless, heat will be lost to the surrounding environment.
Prior art hot melt adhesive application machines typically include electrical resistance heating elements within their supply hoses and applicators to prevent undesirable heat loss from the molten adhesive as it is conveyed from the pumping mechanism to the applicator. However, the typical prior art hot melt adhesive application machine discharge hose and applicators are manufactured to operate on, and are committed to operate on 120 or 240 volt electrical supply systems but not both. Therefore a manufacturer and/or supplier of such equipment must, necessarily, stock machines, discharge hoses and applicators, that operate on one or the other electrical systems.
The present invention overcomes the above described disadvantages of prior art hot melt adhesive application machines.
The present invention teaches an electrically heated main displacement pump body that is partially submerged within the molten adhesive material thereby eliminating the necessity of heating the outside shell of the reservoir. By this technique heat from the submerged pump body first passes, by conduction, into the molten adhesive material and then to the reservoir outer shell. Thus, in heat transfer terms, the reservoir outer shell is the coolest part of the system thereby requiring less insulating material to prevent unnecessary heat loss to the surrounding environment. By the present invention the reservoir container may now be made of a material having a lower heat transfer conductivity than the metal containers of the prior art. For example, the molten adhesive reservoir might be made of a low conductivity resinous material or ceramic.
A further novel feature of the present invention is that the hot melt adhesive pump body, each hot melt supply hose and associated discharge applicator is separately heated by electric resistance heating circuits that may selectively operate on 120 volt or 240 volt AC current.